Conventionally, in the electric shaver, for the purpose of improving a quick shaving performance and improving a skin contact and a fit feeling, there have been proposed a lot of techniques structured such that a shaving portion is provided in a shaving head, and the shaving head is moved in such a manner as to be oscillated with respect to a main body grip held by a hand so as to be brought into close contact with a skin (for example, refer to Japanese Patent Application Laid-Open No. 64-56089 and Japanese Patent Application Laid-Open No. 6-335575).
In Japanese Patent Application Laid-Open No. 64-56089, there is described an electric shaver provided with a swing type shaving head, and the structure is made such that a shaving head is oscillated with respect to a main body grip so as to swing by rotatably installing the shaving head provided with a shaving portion to the main body grip. At this time, the shaving head is rotatably installed in such a manner that a portion near a top portion corresponding to an upper portion of the shaving head forms a center of rotation, on the assumption that the shaving head side is set to an upper side and the main body grip side is set to a lower side, and a gravity point of the shaving head is positioned below the center of rotation. In the structure of Japanese Patent Application Laid-Open No. 64-56089, in the case that the shaving head is unloaded, that is, in a state in which no external force is applied, the shaving head hangs in such a manner that the gravity point is positioned below due to its own weight at a time of setting the main body grip horizontally for getting a shape in a cheek or the like, and there is a problem that it is hard to apply the top portion corresponding to the main shaving portion of the shaving head to the cheer. Further, if it is intended to apply the main body grip to the cheek so as to set the shaving head horizontally for applying a blade surface of the top portion of the shaving head, a moment of rotation is applied to the lower portion of the shaving head due to its own weight, the top portion of the shaving head is detached from the cheek, and a pressing force of the top portion of the shaving head is short, thereby generating a problem that a following performance to the skin is deteriorated.
Japanese Patent Application Laid-Open No. 6-335575 is provided with a means for returning to an initial position for improving the problem that it is hard to apply to the cheek due to the hanging caused by its own weight as mentioned above. This is structured such that a rotating shaft is provided near right and left upper ends of the shaving head provided with a plurality of outer blades, the shaving head follows the skin with respect to various shaving ways by making the shaving head rotatable back and forth around the rotating shaft, a helical torsion coil spring is provided as an elastically deformable elastic body, a head return means is provided for holding the shaving head at an initial position in an unloaded state, that is, a state in which an external force is not applied, and the shaving head is returned to the initial position with respect to the main body grip independent of the empty weight of the shaving head. Accordingly, since the shaving head is maintained at the original position with respect to the main body grip even if the main body grip is set horizontally in the case of applying the top portion of the shaving head to the cheek or an upper lip, it is easy to apply the top portion of the shaving head and a good usability is obtained.
However, in Japanese Patent Application Laid-Open No. 6-335575, it is necessary to make the rotation moment force equal to or more than a force opposing to the moment around the rotating shaft on the basis of the empty weight of the shaving head. Accordingly, a great elastic force is necessary in the helical torsion coil spring, and a rigidity of the helical torsion coil spring becomes high. In other words, since the moment of rotation for returning the shaving head becomes maximum at a time of setting the main body grip horizontally, and the stronger spring force of the helical torsion coil spring is required, the shaving head is hard to be rotated with respect to the rotating shaft at a time of applying the shaving head to the skin so as to get a shave, and there is a problem that it is hard to follow an irregularity of the skin, therefore, a plurality of outer blade portions are not brought into contact with the skin, it is impossible to shave short, and an unshaved portion is left.
Further, since the moment of rotation for rotating with respect to the rotating shaft is large, it is necessary to apply more force to the main body grip for making a plurality of outer blade portions follow at a time of shaving in a direction from the upper lip to the lips so as to strongly press to the skin, it is hard to move the shaving head, and there is a problem that the shaving head does not smoothly slip on the skin.
Further, if the helical torsion coil spring for returning is weakened or the helical torsion coil spring is detached due to the problem mentioned above, the load is strongly applied to the skin from the outer blade portion in a lower side of a plurality of outer blade portions of the shaving head on the basis of the moment of rotation caused by the empty weight of the shaving head by setting the main body grip horizontally at a time of shaving the cheek, the upper lips, and the outer blade portion in an upper side corresponding to the top portion is only weakly applied, so that there is a problem that it is impossible to shave short, and the unshaved portion is left due to a non-contact with the skin.